The art of surveying and mapping has dramatically changed through the use of satellite navigation equipment. Satellite survey devices include receivers that receive position signals from the global positioning system (GPS), Global Navigation Satellite System (GLONASS) receiver or other satellite or pseudolite systems. The satellite position signals are used to compute the position of the receiver.
Survey and GIS (Geographic Information System) applications require extremely high accuracy positions measurements. Due to selective availability (S/A) and environmental conditions, the position signals may be degraded to 100 meter accuracy, which is not satisfactory for Survey and GIS use. Differential correction (DGPS) and real time kinematic (RTK) processes are therefore used to increase accuracy to the within 0.2-5 meter accuracy and centimeter accuracy, respectfully. RTK and real time computation of DGPS both require the use of an additional radio frequency receiver for reception of additional data that is used to compute a corrected, more accurate, position. Thus, the satellite survey device which is typically called the "rover device", includes a range pole for identifying the point for which a location is to be computed, a user input/output device for entry and display of information and data, a satellite receiver and a radio receiver.
Examples of satellite survey devices include the GPS Total Station.RTM. manufactured by Trimble Navigation Ltd. of Sunnyvale, Calif. (GPS Total Station is a registered trademark of Trimble Navigation Ltd.). The GPS Total Station includes a GPS antenna mounted on a range pole. The user places the range pole over the location to be measured. A simplified drawing of this type of surveying equipment is shown in FIG. 1. The range pole 10 has attached to it the antenna 20 for receiving GPS signals and a circular level or vial 30. The user 40 holds the pole 10 and moves the pole 10 about until the level 30 indicates that the pole is vertically oriented and the bottom of the pole touches the location 50 to be surveyed. Once vertically oriented, the information received via the GPS antenna can be used to accurately compute the position of the location 50. Typically, the user will have a backpack 60 that includes a wireless link, such as a radio modem 70, for receiving correction signals from differential GPS (DGPS) base stations. Using DGPS technology, more precise measurements are obtained. The backpack 60 also contains equipment and circuits for generating positional information based upon the signals received through antenna 20 and wireless link 70. The data collection device 100 enables the user to make manual entries, and also provides a visual reading of the survey measurements obtained.
Handheld GPS receivers presently are available on the consumer market. These devices ally marketed towards the recreational sailor or hiker, provide position information accurate to 20-100 meters. Smaller, lighter GPS receivers with survey accuracy would be desirable to surveyors because of ease of transport in the field.
In order to be of utility, surveying data must provide accuracy within the range of 5 mm to 10 or 20 cm. The handheld devices available do not provide this high level of accuracy needed. Thus, it is desirable to provide an accurate handheld device to be used in survey and GIS applications.